Tuesday, 31 August 2010

Seeing is believing? Not so fast there – these 10 amazing animals believe they’re doing mighty fine without seeing their surroundings, so much so that they don’t waste precious resources growing eyes. It’s a strategy that makes, er, sense when living in an environment where vision is impractical, unnecessary and even impossible.

Leptodirus Beetle

So-called troglobites – not to be confused with troglodites, or cave men – are creatures that have adapted their physical forms to best suit the environment of caves, typically to the point where they cannot survive when removed from said caves. The first troglobite to be described in scientific literature was the Leptodirus beetle (Leptodirus hochenwartii), back in 1832.

Leptodirus beetles average about 4/10 of an inch (1cm) in length and are thought to survive by feeding on the carcasses of deceased cave creatures. Found only in several limestone caves in southeastern Europe’s Dinaric Alps, Leptodirus beetles are considered to be a vulnerable species as their ecological requirements span a very narrow range.

Kauai Cave Wolf Spider

The Kauai Cave Wolf Spider (Adelocosa anops), discovered in 1971, can be found on the Hawaiian island of Kauai and inside five caves where only about two dozen in total are thought to live. The caves were formed between 3.6 and 5.6 million years ago so the spider has had several million years to evolve into its current eyeless state – “anops” means eyeless, by the way. The creature relies upon a finely tuned sense of touch and the ability to note minute vibrations when stalking prey within the volcanic caves’ pitch-black environs. That’s a normal Wolf Spider at above right, compared with A. Anops on the left.

Though biologists and environmentalists may bemoan the exceptional rarity of the Kauai Cave Wolf Spider, spelunkers and arachnophobics (or both) might feel the opposite: this intriguing eyeless spider is quite large, measuring over 3 inches (8cm) across. It’s considered to be harmless to humans, if that’s any help when you’re exploring the deepest depths of a Kauai cave and the battery in your flashlight dies.

Living mainly in Kentucky’s famed Mammoth Cave and other subterranean caves in the area, the Kentucky Cave Shrimp is considered to be endangered due to above-ground dams and canals that have affected the natural rate of water flow and sedimentation in the Mammoth Cave system. The shrimp, which are both eyeless and transparent, grow to a length of 1.25 inches (3.15cm) and are closely related to other cave-dwelling shrimp found in Texas, Alabama and Florida.

The rarity of the Kentucky Cave Shrimp and the fact that its existence is threatened by groundwater pollution has made the shrimp somewhat of a poster-child for environmental activism and a local cause celeb in the area of Mammoth Cave. In 2009, the newly formed Bowling Green baseball club staged a Name The Team contest and although “Hot Rods” was the winning (or at least, chosen) entry, Cave Shrimp received at least some votes. Pity it didn’t win – just imagine the above awesome logo on players’ uniforms.

Blind Cave Crayfish

Almost 40 different species of Cave Crayfish live in various cave ecosystems scattered across the United States alone. Common to most of these species is eyelessness, lack of pigmentation and very long lifespans – in some cases estimated at over 75 years! Cave Crayfish are among the largest troglobites, reaching lengths of almost 4 inches (10cm).

Cave Crayfish have evolved over millions of years to be totally in sync with their exceptionally demanding environment. As such, they can be looked at as “canaries in the coalmine” – environmental indicators as to the health of the pristine, naturally filtered groundwater in which they live.

Blind Cave Crab

Like many troglobites, Cave Crabs exist in dark, flooded cave environments around the globe. They share a number of common evolutionary adaptations, such as eyelessness and depigmentation that gives them a ghostly appearance – not that anyone (or anything) saw them before humans with lights and cameras invaded their space.

Cave Crabs are often found around the inlets where freshwater enters caves, bringing with it food for the opportunistic crabs to eat. The Cave Crab in the topmost image above, Sesarmoides jacobsoni, was discovered in a cave located on the Indonesian island of Java.

Blind Cave Fish

The Blind Cave Fish, or Mexican Tetra (Astyanax mexicanus) has evolved from normal Tetra fish that can be found today in the Rio Grande river and other rivers and streams in Mexico and Texas. Growing to about 4 inches (10cm) in length, the Mexican Tetra displays extreme albinism, a semi-transparent skin and most shocking: complete eyelessness. Such traits are shared by the newly discovered blind cave fish Milyeringa veritas (above, lowest photo), a 2-inch (5cm) long eyeless fish found in Australian freshwater aquifers.

Mexican Tetras are one of the only cave-dwelling troglobitic creatures that are not endangered – they can even be bought and maintained as unique aquarium fish! Owners report that though completely blind, Mexican Tetras kept in aquariums use their highly developed non-visual sense organs to avoid bumping into aquarium objects and walls, and

Brazilian Blind Characid

Stygichthys typhlops, a blind relative of the fearsome piranha, may be “the most threatened underground fish species in Brazil” according to ichthyologist Dr. Cristiano Moreira of the Federal University of Sao Paulo. The fish lives in a single, 15.5 mile (25km) long aquifier in the Brazilian state of Minas Gerais.

Villagers drawing water from wells in the town of Jaiba reported seeing strange pale fish swimming in the well. Maybe it’s just me but when you’ve got piranhas in the well it’s time to think about moving, amiright?

Texas Blind Salamander

The Texas Blind Salamander (Eurycea rathbuni) is an extreme example of eyelessness as an adaptation to low or zero light conditions in underground environments. Growing up to 5 inches (13cm) in length, this rare and unusual creature is found in just one location: the San Marcos Pool of the Edwards Aquifer in Hays, Texas.

Olm

The Olm (Proteus anguinus) is the only member of its genus and the only troglobitic vertebrate on the European mainland. Like the Leptodirus beetle, it can be found in the freshwater caves of southeastern Europe’s Dinaric Alps. First described in 1768 but not recognized as a purely cave-dwelling animal, the Olm is known to people in Slovenia and Croatia as the “human fish” due to its pale, pinky coloration.

The Olm’s snakelike body averages 8 to 12 inches (20–30 cm) in length with occasional examples reaching 16 inches (40cm). As one of the symbols of Slovenia, the Olm was featured on some of the country’s coins before they switched to the Euro.

Though it may superficially resemble the Texas Blind Salamander and like it is completely eyeless, the Olm is a completely different animal. It is neotenic, remaining in the gill-breathing larval stage its entire life (which may be as long as 100 years!). Olms also have 3 toes on the forelimbs but only 2 on their hind limbs. Here’s a short video on the Olm from the acclaimed PBS television program Nature:

Madagascar Blind Snake

The Madagascar Blind Snake (Xenotyphlops mocquardi) is one of 15 different kinds of blind snakes that call Madagascar their home, though Xenotyphlops takes sightlessness to a whole new level. In fact, unless this 10-inch (25cm) long, pencil-thin burrowing reptile opens its mouth – or happens to be in motion – it’s tough to know which end is which. While not eyeless per se, the Madagascar Blind Snake is negatively phototaxic, meaning it avoids light and when brought to the surface immediately tries to burrow back underground. Xenotyphlops and its blind relatives are the only snakes that eat insects exclusively, homing in on ant and termite nests with a highly developed sense of smell.

The Madagascar Blind Snake was actually discovered twice: once in 1905 and again one hundred years later after not being seen at all in the interim. It obviously has perfected the art of deception; the genus is believed to have split off from its ancestral line about 155 million years ago when Madagascar was part of the composite Gondwanaland continent.